In forestry operations, cut trees are moved from the felling area to a roadside or other desired transport location. The logs are dragged on the ground by a mainline connected to a traction machine or by a mainline overhead yarding system which carries the logs in a suspended or partially suspended manner. Steel cables extending from the mainline form a noose or choker. The choker cable is looped around one or more trees by the chokerman and is fastened back onto itself by securing a ferrule, on the end of the choker cable, in a choker hook. This allows the choker cable to tighten around the tree. Tension is then applied to the mainline to pull or lift the tree and move it from the felled position to a desired transport location.
When the tree has been moved, the choker must be released to free the tree. Prior art required that this task be accomplished manually by a chaser who slackened the choker cable and released the choker hook. The manual unhooking operation is dangerous and time consuming.
The advantages of self releasing chokers have been attractive and some such chokers are disclosed in Canadian Patent 1,225,416 (Vodors), U.S. Pat. No. 5,064,235 (Selby) and U.S. Pat. No. 5,064,235 (Lessard). These chokers, however, are complex and/or costly.
It is, therefore, an object of this invention to provide a choker hook which, when the choker hook is in a first position and the log is being transported from its felled position to its desired transport position, is of a configuration such that the pulling force on the choker cable tends to bias the ferrule of the choker cable into its locking position in the choker hook. When the direction of pull on the log and the choker cable changes, the choker hook rotates or pivots through a predetermined angle and about predetermined axes and assumes a second position where the direction of pull in the choker cable tends to remove the ferrule from its locking position.
The above object is likewise described in our U.K. provisional application Serial No. 9319472.8 filed Sep. 21, 1993, entitled AUTO RELEASE CHOKER and naming J. Brent McPhee as inventor.